1. Technical Field
The present invention relates to a liquid jet apparatus adapted to form predetermined characters and images by emitting microscopic droplets of liquids from a plurality of nozzles to form microscopic particles (dots) thereof on a medium.
2. Related Art
An inkjet printer as one of liquid jet printing apparatuses using a liquid jet apparatus can generally provide low-price and high quality color prints with ease, and therefore has widely been spreading not only to offices but also to general users along with widespread of personal computers and digital cameras. Some of such liquid jet apparatuses have a plurality of nozzles for emitting liquid jets, provided to a liquid jet head, each of the nozzles being provided with an actuator such as a piezoelectric element, and drive each of the actuators of the liquid jet head with a drive signal composed of waveform voltage signals, thereby emitting liquid jets from the corresponding nozzles towards a medium.
As power amplification of such a drive signal, the liquid jet apparatus described in JP-A-5-77456 is arranged to analog-convert a drive waveform signal forming a basis of a signal for controlling driving of the actuator with a D/A conversion circuit, and then power-amplify the analog drive waveform signal with an analog power amplifier, Further, the liquid jet apparatus described in JP-A-11-204850 is arranged to analog-convert the drive waveform signal with a D/A conversion circuit, then pulse-modulate the analog drive waveform signal, and then power-amplify the modulated signal with a digital power amplifier.
Incidentally, piezoelectric elements used as actuators of inkjet printers are charge-discharge actuators, and therefore, the drive signal charges the charge-discharge actuators and discharges the charge-discharge actuators. A digital power amplifier of the liquid jet apparatus described in JP-A-11-204850, although having an advantage of low loss and low heat generation, is provided with a low pass filter for smoothing the drive signal inserted on the output side thereof, and has a configuration of coupling the capacitance of the charge-discharge actuator to the low pass filter, and therefore, the waveform of the drive signal varies with the number of actuators coupled thereto. In contrast, the analog power amplifiers do not have low pass filters on the output side, and therefore, the waveform of the drive signal does not vary even if the number of actuators coupled thereto varies.
However, the analog power amplifier for charging the charge-discharge actuator and discharging the charge-discharge actuator is composed of a charging transistor and a discharging transistor push-pull coupled to each other, and amplifies the drive signal using a high power-supply voltage with linear driving, and therefore, has a large difference in voltage between the power supply voltage and the drive signal for charging the charge-discharge actuator and a large difference in voltage between the drive signal for discharging the charge-discharge actuator and the ground voltage, and accordingly has large power consumption. Since the power consumption is mostly consumed as heat, the drive circuit for generating the drive signal requires a large-sized transistor and a heat sink, the mounting area on the circuit board becomes extremely large, and in particular the size of the heat sink causes difficulty in the layout,